1. Field of the Invention
The present invention relates generally to a path setting control system in a communication network. More specifically, the invention relates to a path setting control system which can recover fault by a distributed self-healing system for faulty network recovery upon occurrence of link failure in a communication network including a plurality of nodes.
2. Description of the Related Art
As one of fault recovery system in a communication network is a distributed self-healing system for faulty network recovery. When failure is caused in a targeted path, alternating operation is performed at both end nodes, at which the path are terminated. Therefore, when the failure is caused at a portion where the terminal node of the path cannot detect directly it becomes necessary to designate alternation of its path to the terminal nodes by the nodes at both ends of the faulty portion.
FIGS. 13(A) to 13(C) are explanatory drawings showing the prior art. In FIGS. 13(A) to 13(C), A, B, C, D, E and F represent nodes. A path 1 is a path set between the nodes A and E. It is assumed that, upon setting the path 1, a path ID which is a path identifying information for identifying the path 1 in the network, and a version identifying number of times of connection of the path are notified to relay nodes B, C and D.
For example, as shown in FIG. 13(A), when failure is caused at two portions of the path between the nodes B and C and between C and D, the nodes B, C and D at faulty ends for alternating the path 1 transmit an alternation designating message 100 for alternating path 1 to the terminal nodes A and E. When the alternation designating message 100 is received, the terminal nodes A and E transmits release message to command release of the path 1 to the relay nodes. The nodes B and D receive the release message and release the path 1. However, since the release message does not reach the node C, the setting of the path 1 is maintained in the node C.
Subsequently, the nodes A and E modify the version of the path 1 and initiate alternation of the path 1. Then, the alternated path is established via the node F, as shown in FIG. 13(B). Then, as shown in FIG. 13(C), when failure is recovered only between the nodes B and C after completion of alternation, since the preceding version of setting is remained in the node C, the node C transmits the alternation designating message 100 is transmitted to the node A for failure between the nodes C and D. Because of difference of version, the node A receiving the alternation designating message from the node C ignores the designation for alternation. Therefore, since alternating operation will not be performed again for the path 1 through which normal communication has already been established, communication through the path 1 may not be interrupted.
However, in such prior art, as shown in FIG. 13(C), despite of the fact that the path 1 has already been alternated through the node F, assignment of the transmission path of the node B and C is maintained in the node C, new path between the nodes B and C cannot be established for lack of band in the transmission path between the nodes B and C. Therefore, efficiency of use of the transmission path can be lowered.